用css做一个加号

<div class="plus-icon"></div>

.plus-icon {
  width: 20px;
  height: 20px;
  position: relative;
  background-color: #000;
}

.plus-icon::before,
.plus-icon::after {
  content: "";
  position: absolute;
  background-color: #fff;
}

.plus-icon::before {
  width: 2px;
  height: 12px;
  top: 4px;
  left: 9px;
}

.plus-icon::after {
  width: 12px;
  height: 2px;
  top: 9px;
  left: 4px;
}